A hypodermic needle entering into a patient's body is invariably contaminated by the patient's blood and body fluids. Following use of the needle, the needle presents a risk to physicians, nurses, and other health care personnel because the needle might transmit an infection or disease to such personnel if it were to accidentally puncture them. Thus, health care personnel are in constant danger of contracting infections and diseases, some of which may be deadly. Other potential victims of accidental needle punctures include sanitation workers who later dispose of garbage containing the hypodermic needles. Often a needle puncture in a person's skin is so trivial that it remains unrecognized until the person becomes seriously ill. The diseases which may be transmitted by a contaminated hypodermic needle include Immune Deficiency Virus, Hepatitis, Rabies, Cure, Encephalitis, and Arbor viruses. The outcome of contracting one of these diseases is often fatal because there are no known cures for any of these diseases.
The problem of accidental needle punctures is well recognized, and enormous inventive effort has been devoted to concealing the sharp needle point of hypodermic needles. One such effort is described in the present applicant's U.S. Pat. No. 5,338,311, issued Aug. 16, 1994, and U.S. Pat. No. 5,514,100, issued May 7, 1996. A hypodermic needle has many applications in modern medicine. One application is to fit the hypodermic needle onto a syringe so that the needle can be inserted into a person's body or vein to obtain samples of tissue or blood for examination. To obtain multiple samples for different tests, a double-ended hypodermic needle is attached to the syringe barrel. One sharp end of the needle is used to puncture the vein of the patient, while the other sharp end projects inside the syringe barrel. A pre-vacuumed test tube with a rubber stopper is forced on the needle end inside the barrel. Puncture of the rubber stopper results in the withdrawal of a blood sample into the test tube because of the preexisting vacuum. The test tube containing the blood sample is then withdrawn, and another test tube intended for a different test is forced into the barrel to collect a second sample in an identical manner. The barrel with the attached needle is disposed of in its entirety, but during its transport to final destruction it may cause accidental needle sticks and transmit diseases.
The double-ended needles pose special problems because retraction of one sharp end can result in the projection of another sharp end toward the user. Further, the needle may be screwed to the end of the barrel, which makes retraction of the needle difficult or impossible.